Variable resistor with high torque adjustment



A. M. DAILY June 18, 1957 VARIABLE RESISTOR WITH HIGH TORQUE ADJUSTMENTFiled Jan. 11. 1954 iwwfid Arihyr MDaIZy 4 2,796,501 Patented June 18,1957 VARIABLE RESISTOR WITH HIGH TORQUE ADJUSTMENT Arthur M. Daily,Edwardsburg, Mich., assignor to Chicago Telephone Supply Corporation,Elkhart, Ind., a corporation of Indiana Application January 11, 1954,Serial No. 403,163

7 Claims. (Cl. 201-55) This invention relates to variable resistors ofthe type commonly employed in radio and television receivers and has asits general purpose to provide a variable resistor especially adaptedfor use in apparatus which is apt to be subjected to considerablevibration, as for iustancethe communication receivers of airplanes andthe like. In such situations the ordinary variable resistor does notafford adequate assurance against unintentional changes in setting. Therelatviely light resistance to rotation of its contactor leaves it proneto creep from a selected position of adjustment. Accordingly, some meansmust be provided to increase the torque necessary to effect adjustmentof the resistor if it is to be satisfactory for use in apparatus apt tobe subjected to serious vibration.

The broad concept of providing some means to elfect this purpose is notnew with this invention, but heretofore the incorporation of additionalfrictional resistance to adjustment has involved additional parts whichnot only increased the cost of the unit due to the added assembly timebut in general was found to be rather makeshift and objectionable.

It is, therefore, the purpose of this invention to provide an improvedmanner of incorporating additional frictional resistance to adjustmentof the resistor which eliminates all additional parts and therefore innowise increases the cost of assembly, and because of its reduction inthe number of parts achieves desirable simplicity.

More especially it is an object of this invention to incorporate themeans for increasing the resistance to adjustment of the resistor in thestop plate of the rotating assembly of the unit, in the form of springarms formed integrally with this plate and bearing against the end wallof the metal shell which forms part of the housing for the resistor.

With the above and other objects in view, which will appear as thedescription proceeds, this invention resides in the novel construction,combination and arrangement of parts substantially as hereinafterdescribed and more particularly defined by the appended claims, it beingunderstood that such changes in the precise embodiment of the hereindisclosed invention may be made as come within the scope of the claims.

The accompanying drawing illustrates one complete example of thephysical emboiment of the invention constructed according to the bestmode so far devised for the practical application of the principlesthereof, and in which:

Figure 1 is a longitudinal sectional view through a variable resistorembodying this invention; and

Figure 2 is a perspective view of the rotating assembly of the resistorillustrating particularly the combination stop plate and spring frictionarms.

Referring now particularly to the accompanying drawing, the numeral 5designates the base of the resistor which as is customary is a generallycircular disc of suitable insulating material. Fixed in this base is ametal thimble 6. The securement of the thimble also holds a metal groundplate 7 in position over the outer face of the base. The major portionof the thimble lies at that side of the base at which the ground plateis located and as is customary is threaded to receive clamping nuts (notshown) by which the entire unit may be mounted on a supporting panel.The opposite end of the thimble protrudes a short distance beyond theinner face of the base to provide a thrust bearing 8.

A flat split ring-shaped resistance element 9 is. mounted on the innerface of the base concentrically to the thimble and, as is customary, hasterminals electrically connected thereto and attached to the base, oneof said terminals being illustrated and indicated by the numeral 10.Also overlying the inner face of the base is a collector ring 11 whichhas a terminal 12 formed integrally therewith and mounted on the base inthe customary manner. The collector ring, like the resistance element,is concentric to the thimble and is encircled by the resistance element.

Spring contact fingers 13 and 14, respectively, traverse the resistanceelement and collector ring upon rotation of a control shaft 15 journaledin the thimble. The spring contact fingers 13 and 14 are mounted on aninsulated drive arm 16 which, in turn, is rightly fixed to the shaft bybeing clamped between a shoulder 17 and a metal stop plate 18 fixed tothe shaft by having the extremity of the shaft riveted or swedgedthereover as at 19.

A C-washer 20 mounted in a groove in the shaft and arranged to bearagainst the adjacent outer end of the sleeve limits axial movement ofthe shaft and the rotating assembly carried thereby in the direction inwhich the tension of the spring contact fingers 13 and 14 urge the same.The C-washer thus serves to hold the shaft and the parts carried therebyassembled with the base.

The instrumentalities of the, variable resistor are enclosed in ahousing formed by the base 5 and a cupshaped metal shell 21 having aflat end wall 22 and a cylindrical side wall 23, the latter beingconnected to the base in thecustomary manner with the end wall 22 inparallel spaced relation to the inner face of the base.

The metal stop plate 18 has a fiat hub portion '24 from whichdiametrically opposite flat arms. 25 and 26 extend. The arm 25 has itsextremity bent outwardly as at 27 to provide a stop lug which coactswith an abutment 28 on the cylindrical wall of the metal shell to definethe limits of rotation of the rotating assembly.

The diametrically oppositely extending arms 25 and 26 have curved springarms 29 formed integrally therewith and projecting substantiallycircumferentially from opposite sides thereof. Thus, as will no doubt beclear, at the time the stop plate is blanked out the spring arms arecoplanar with and embrace the circular hub portion 24, but thereafterthe spring arms are sprung or formed to project from the plane of thehub portion 24 in the same direction as the stop lug 27.

The outer extremities of the arms are diametrically opposite one anotherand terminate on a common plane parallel to the flat hub portion butspaced outwardly thereof a distance greater than the height of the stoplug 27 and even greater than the space between the inner surface of theend wall 22 and the hub portion 24. Thus, when the cover or shell 21 isassembled with the base, these arms are depressed. Two points offrictional engagement are thereby established between the rotatingassembly of the control and its cover or shell, and to assure smoothadjustment of the resistor the extremities of the spring arms arepreferably formed with smooth convex contact surfaces 30.

Since the spring arms are of the same length and under the same springtension the end thrust imposed upon the rotating assembly by theirdepression is balanced at diametrically opposite sides of the axis ofrotation. This semblyby the spring fingers 13 and 14 and, therefore,

must be positively resisted to prevent excessive contact pressure. onthe resistance element and collector ring. To this 'end'the insulateddrive arm 16 bears against'jthe thrust bearing 8 provided by theadjacent inner end ofthe thimble. r j

From the foregoing description taken in connection with the accompanyingdrawing it will be readily apparent to those skilled in this art thatthe frictional engagement between the contact surfaces 30.0f the springarms 29 and the back wall 22 of the cover or shell effectually resistsrotation of the control shaft and thus increases the torque necessary toeffect adjustment of the resistor. It will also be seen that thisinvention achieves the desired resistance to adjustment of a variableresistor and thus attains its objective in an extremely simple mannerand without the need for increasing the number of parts beyond thatcustomary in variable resistors of this type.

What I claim as my invention is:

l. A variable resistor of the type having a base of insulating materialwith a resistance element mounted thereon to be traversed by a contactordriven by a rotatable control shaftwhich passes through the base, andwherein the base coacts with a cup-shaped metal shell connected theretoto provide a housing for the instrumentalities of the variable resistor,and the end wall of the cup-shaped shell overlies the base in spacedrelation thereto, characterized by the fact that: the. operating shafthas a metal stop plate fixed to the end thereof within the housing andlying between the contactor and the end wall of the cup-shaped shell,which stop plate has a portion thereof positioned to engage with ashoulder on the inside of the housing to limit rotation of the shaft andthe contactor driven thereby; and further characterized by the provisionof spring finger means formed as an integral part of said stop plate andbearing against the inner face of the end wall of the metal shell withsubstantial spring force to thereby urge the stop plate forwardlytowards the contactor and frictionally resist rotation of the controlshaft and the contactor driven thereby.

2.'A variable resistor especially adapted for use in locations subjectto excessive vibration, comprising: a base of insulating material; aresistance element mounted on the base; a rotatable control shaftpassing through the base; a contactor fixed to the control shaft to bedriven thereby and to traverse the resistance element in response torotation of the control shaft; a stamped cup-shaped metal shell fixedwith respect to the base andcoacting therewith to provide a housing forthe instrumentalities of the variable resistor, said shell having an endwall opposite the base; a metal stop plate fixed to the control shaft;cooperating abutments on the metal shell and said stop plate to definethe limits of rotation of the shaft and the contactor driven thereby;and a pair of spring arms formed integrally with said metal stop plateand projecting towards the end wall of the shell, the outer extremitiesof said arms bearing against the inner face of the end wall of the shellto thereby place said arms under spring tension and frictionally resistrotation of the shaft and the contactor driven thereby.

3. The variable resistor of claim 2 further characterized by the factthat the resilience of said spring arms urges the contactor intoengagement with the resistance element; and further characterized by theprovision of a thrust bearing means on the base and the rotatingassembly to resist the end thrust imposed upon the rotating assembly bysaid spring arms.

4. In a variable resistor: a base of insulating material;

a metal thimble fixed in said base with one end thereof projecting ashort distance from one side of the base and its opposite end projectinga greater distance from the other side of the base; a resistance elementmounted on the first side of the base concentrically to the axis of thethimble; a control shaft journalled in the thimble; an insulated drivearm fixed to the control shaft and bearing against the first named endof the thimble to thereby limit axial movement of said arm and the shaftin the direction to carry said arm toward the base; a contactor on theunderside of said insulated drive arm bearing against the resistanceelement; a metal stop plate fixed to the shaft and overlying the otherside of the insulated drive arm; a housing for the resistor including anend wall overlying the base and the rotating assembly carried by theshaft and spaced a definite distance from the stop plate; cooperatingstop abutments on the housing and the metal stop plate to limit rotationof the shaft and rotating assembly; and spring arms integral with saidstop plate, said spring arms being confined under tension between theinner face of said end wall and the stop plate and bearing against theend wall at equal radial distances from the axis of rotation to therebyhold the rotating assembly against its thrust bearing and frictionallyresist rotation thereof.

5. In a variable resistor of the type comprising a housing having a pairof spaced apart, substantially parallel end walls, through one of whicha rotatable control shaft projects and on one of which a resistancestrip is mounted for engagement by a rotatable contactor carried by theshaft: a pair of flexible arms carried by the shaft and having endportions frictionally engaged with the end wall of the housing oppositethe wall on which the resistance strip is mounted at diametricallyopposite points spaced equal distances from the axis of the controlshaft to frictionally resist rotation of the shaft.

6. The variable resistor of claim 5 further characterized by abutmentmeans on the shaft engaged with an opposing abutment fixed on said wallthrough which the shaft projects to resist axial displacement of theshaft away from said opposite end wall of the housing against which saidflexible arms are engaged to thereby maintain said rotatable contactorunder constant tension and thus assure uniform contact pressure betweenthe contactor and the resistance strip.

7. In a variable resistor of the type comprising a housing having acylindrical side wall and pair of spaced apart substantially parallelend walls, through one of which the control shaft of a rotatableassemblyprojects and on one of'which a resistance strip is mounted forengagement'by a rotatable contactor which forms part of the rotatableassembly: a stop plate fixed to the shaft; cooperating stop abutments onthe housing and on said stop plate to limit rotation of the rotatableassembly; a spring arm integral with said stop plate and having aportion biased into frictional engagement with the end wall of thehousing opposite side end wall on which the resistance strip is mountedto thereby resist rotation of the shaft; and abutment means on the shaftengaged with opposing spaced apart abutments fixed on said wall throughwhich the control shaft projects to confine the shaft against axialdisplacement.

References Cited in the file of this patent FOREIGN PATENTS

